This invention relates to microwave (including millimeter wave) devices, and, more particularly, to microwave phase modulation with a liquid crystal-based composite material.
The index of refraction of many media is fixed and essentially constant, but there are "birefringent" media where the index of refraction of the material varies with relative orientation of a polarized wave and the medium. The birefringence of a uniaxial crystal is manifested by double angular displacements of a wave that passes through the medium. For example, in many viewing angles calcite crystals are birefringent to visible light, so that two differently positioned images are often seen when an object is viewed through a calcite crystal.
The index of refraction of some birefringent materials and of Kerr-effect isotropic materials can be controllably varied directionally by the application of a magnetic or electrical field to the medium. For example, liquid crystals are known to be birefringent for visible light, and variable under the application of an electric field. This property has been used in liquid crystal light valves for use in color projection displays.
Although birefringent materials have been known and used for controlling visible light, there are many potential applications for such materials in other portions of the electromagnetic spectrum such as the microwave range. Although viable birefringent and Kerr-effect materials are known for use in the visible-light frequency range, until recent years there have been known few if any practical Kerr-effect materials for microwave radiation. The most promising reported Kerr-effect materials for use in the microwave range are suspensions of highly asymmetric metallic particles in organic liquids. The birefringence of these suspensions is typically about 0.08 or less.
Although such media having controllable indices of refraction to microwaves are known, there is a need for media with increased birefringence to control beams of microwave energy, in applications such as scanning array antennas. The greater the birefringence, the more readily a device can be made to achieve a preselected degree of beam control. Moreover, the cost of the medium and the control mechanism for many existing microwave modulators is so high that they cannot be used in applications that require large arrays or must be low cost to be commercially feasible. The present invention fulfills the need for an improved microwave-birefringent material which can be controlled with applied electric and magnetic fields, and further provides related advantages.